Conventionally, it is well known that a fuel injection valve has a valve component which is accommodated in a valve housing, whose valve seat surface tapers toward a downstream side from an upstream side with respect to an injection hole that injects fuel. In such a fuel injection valve, the valve component biased by an elastic component is separated from or seated on the valve seat surface for valve opening or valve closing, allowing intermittent fuel injection from the injection hole.
For example, a valve component of a fuel injection valve disclosed in Patent Literature 1 has an inner tapered surface having a large taper angle and an outer tapered surface having a small taper angle continuing to an outer peripheral of the inner tapered surface, and the boundary portion between the tapered surfaces is separated from or seated on a tapered valve seat surface. A valve component of a fuel injection valve disclosed in Patent Literature 2 has a convex curved surface curved in a partial spherical shape with a predetermined curvature radius, and an intermediate portion in a radial direction of the convex curved surface is separated from or seated on a tapered valve seat surface.
However, in the fuel injection valve disclosed in Patent Literature 1, the boundary portion between the inner tapered surface and the outer tapered surface protrudes sharply toward the valve seat surface. In the valve component biased toward the valve seat surface by the elastic component, therefore, the sharp boundary portion collides with the valve seat surface during valve closing operation, which excessively increases dynamic contact pressure generated between the boundary portion and the valve seat surface. Such an increase in dynamic contact pressure results in wear of the boundary portion and the valve seat surface, which may cause fuel leakage from between the boundary portion and the valve seat surface in a valve closed state after the valve closing operation.
In the fuel injection valve disclosed in Patent Literature 2, the smooth convex curved surface having a partially spherical shape is seated on the valve seat surface to establish a valve closed state. Hence, the static contact pressure generated between the convex curved surface and the valve seat surface is also reduced in the valve closed state of the valve component biased toward the valve seat surface by the elastic component. Such a reduction in static contact pressure undesirably tends to cause fuel leakage from between the boundary portion and the valve seat surface in the valve closed state.
In particular, when fuel is injected at a relatively low fuel pressure into an intake port of an internal combustion engine and thus the valve component is pressed toward the valve seat at a decreased force due to the low fuel pressure, the fuel leakage conspicuously may occur.